Pipe anchor



C F. JOHNSON July 2, 1963 PIPE ANCHOR ll Sheets-Sheet 1 Original FiledMay 14, 1954 INVENTOR.

n a J n M d E J M [M 5 ATTORNEY July 2, 1963 Original Filed May 14, 1954C. F. JOHNSON PIPE ANCHOR 11 Sheets-Sheet 2 BY ATTOfi/Vf V Char/e5 fL/O/IUJO INVENTOR.

C. F. JOHNSON PIPE ANCHOR July 2, 1963 11 Sheets-Sheet 3 Original FiledMay 14, 1954 Char/es f. dob/won INVEN TOR.

ATTORNEY C. F. JOHNSON PIPE ANCHOR July 2, 1963 11 Sheets-Sheet 4Original Filed May 14, 1954 C. F- JOHNSON July 2,1963

PIPE ANCHOR 11 Sheets-Sheet 5 Original Filed May 14, 1954 Char/es 54/0/20; on

INVENTOR.

C. F. JOHNSON PIPE ANCHOR July 2, 1963 11 Sheets-Sheet 6 Original FiledMay 14 1954 ATTORNEY July 2, 1963 vc. F. JOHNSON 3,095,627

PIPE ANCHOR Original Filed May 14. 1954 11 Sheets-Sheet 8 (bar/e: /-TJohnson INVENTOR.

ATTORNEY July 2, 1963 c. F. JOHNSON 3,095,627

PIPE ANCHOR ll Sheets-Sheet 9 Original Filed May 14, 1954 Char/es EJohnson INVENTOR.

ATTORNEY July 2, 1963 c. F. JOHNSON PIPE ANCHOR ll Sheets-Sheet 10Original Filed May 14, 1954 July 2, 1963 c. F. JOHNSON PIPE ANCHOR 11Sheets-Sheet 11 Original Filed May 14, 1954 bar/e5 l. L/0/7/7J onINVENTOR.

BY it: A rro/swz Y Q United States Patent Office I 3,095,627 PatentedJuly 2, 1963 11 Claims. (Cl. 24-263) This invention pertains to wellsand more particularly to anchoring devices used therein, e.g. devicesfor suspending casing from a well head, devices for holding a packer inposition in a casing, devices for connecting a fishing tool to a fish asin spears and overshots.

More specifically, the invention pertains to anchoring devices of thetype utilizing slips for engaging a pipe and transferring load betweenthe pipe and the support for the slips.

A slip is a wedge having a pipe engaging or front face which is agenerally cylindrical surface with means such as sharp circumferentiallyextending teeth thereon to engage a pipe by indentation of the surfacethereof suflicient to prevent relative axial motion of the pipe andslip, the back face of the wedge, which faces away from the pipe beingtapered, that is, having a surface which is at an angle to the axis ofthe cylindrical front face. Usually the back face of the slip is conicalwith the cone axis concentric with the axis of the cylindrical frontface. Slips are also known in well apparatus having plane back faces;however, where a plurality of slips are used disposed around the outsideor the inside of the pipe to be engaged as shown in the embodiments ofthe invention hereinafter illustrated, as a practical matter havingreference to the maximum utilization of the available space, the backfaces of the slips will have generally conical surfaces. According towhether the slips are to engage the interior or exterior of the pipe,the cylindrical front faces thereof will be convex or concave and theconical back faces thereof will be concave or convex, just the oppositefrom the front faces.

Usually a slip is an integral construction. However, composite slips arealso known, as shown for example in United States Patent Number2,061,771 issued April 4, 1936, to George T. 'McLagan. Therefore a slipmay be considered to be a combination of pipe engaging means, supportengaging means, and means for transferring load between the pipeengaging means and the support engaging means. p 7 Also, slips areusually arcute segments of one hundred twenty degrees or less and usedin sets circumferentially disposed around the pipe to be engaged, withspaces between the sides of the slips to permit them to move radially inand out. However, slips are also known of greater than 360 degreesextent such as shown for example in United States Patent Number2,670,797 issued March 2, 19-54, to A. L. Armentrout.

Difiiculty has been experienced with slip suspension of well casing whenthe casing is of great weight, as in very deep wells, the difiicultybeing a tendency of the casing to collapse or bottle neck. Similartroubles may be encountered in the-use of overshot fishing tools ifgreat forces are required to free the fish. The reverse type of problemmay be encountered with spears and packers where excessive axial loadingmay cause bursting of the fish or casing as the case may be.

The most important application of the invention is in slip suspension ofcasing in a casing head and this example will be discussed in thefollowing, bearing in mind that the theory is of general application. Inthis illustrative case it is desired to reduce the final radial unitpressure of the slips on the casing for any given weight of easing sothat the reduction in casing diameter will not exceed the maximumpermissible value for-the maximum Weight of easing that can be hung inthe well.

The terminology final radial unit pressure is used because the hangingof casing by means of slips is not an instantaneous process but occupiesa brief period of time and initially the only radial force acting on thepipe is that due to the weight of the slips and the friction between thecasing and slips as the casing is lowered. It is only after the pipegripping teeth (wickers) on the front faces of the slips havesufficiently indented the pipe to hold it against relative motion thatthe full final radial force of the slips on the pipe is exerted.

The maximum permissible reduction of casing diameter may be determinedby the necessary clearance for passage-of full gage tools therethroughas is necessary for performing operations inside the casing after it ishung. Another determining factor is that the reduction in diameter mustnot be such as to correspond to stresses exceeding the yield pointwherein further plastic deformation occurs without increased loadingresulting usually in the casing pulling apart. Which of these twofactors is controlling will depend on the strength and thickness of thecasing wall.

The maximum weight of easing that can be hung in a well is to be judgedby the strength of the coupling joints. It is desirable that the slipsuspension be such as to permit a weight of casing to be hung equal tothe coupling strength without exceeding the maximum permissiblereduction in casing diameter.

Two possible ways of reducing the final radial unit pressure of theslips on the casing are increase of area of contact of slips and pipe tobetter distribute the load and reduction of the total radial componentof the slip force against the pipe. When either of these methods istried, difficulties are encountered as will be explained.

The radial component of the slip force on the pipe is equal and oppositeto the radial component of the pipe reaction on the slips. Aconsideration of the forces in equilibrium acting on a slip as a freebody will therefore be helpful in investigating the problem. The forcesacting on a slip supporting a casing from a casing head consist of theweight of the slip, the reaction of the pipe, and thereaction of thesupporting bowl in the casing head; the slip transferring load from thepipe to the bowl. After the casing has been hung the weight of the slipsis negligible compared to the other forces involved, so that there mustbe equilibrium established between the pipe reaction and the bowlreaction. Since the radial component of the pipe reaction must be equaland opposite to the bowl reaction, we can turn our attention to thelatter.

There being sliding contact between the back of the slip and the bowl,the bowl reaction may be resolved into two components, one normal to thebowl and a friction component parallel to an element of the surface ofthe bowl. Therefore the radial component of the bowl reaction will bereduced as the taper angle of the bowl increases and as the frictionangle of the bowl increases, the latter angle being the angle whosetangent is the coefficient of friction between slip and bowl.

It has been determined mathematically that the answer to the foregoingproblems does not lie in increased taper on the backs of the slips, forthis reduces the length of the slips and causes corresponding increasedunit stress on the pipe contacted by the front of the slips. In thisconnection it is to be noted that in wells the radial distances arefixed which is the reason increased taper means shorter slips. Likewise,increased length of slips with more gradual taper is not the answerbecause the radial forces tend towards infinity as the taper approachesI 3 Zero, so that although contact area between slips and pipe isincreased with longer slips, the unit stress remains the same orincreases. Again it is to be observed that in a well where radialdistances are fixed, increased length requires less taper on the slips.

One solution of the problem has been the use of step backed slips inorder to overcome the limiting factor of radial distance in the well.With such slips greater length can be achieved without reduction oftaper. This solution of the problem presents manufacturing difiicultiesbecause of the necessity of aligning the successive steps on the slipbacks so as to make them all seat at once. The close tolerances requiredcause the cost to be high. Furthermore, if, through manufacturing error,tolerances are not maintained, all of the tapered portions on the backsof the slips will not seat simultaneously resnlting in a slip of shorteffective length which will cause the pipe to be collapsed or burst asthe case may be. This solution of the problem may therefore beconsidered to be unreliable.

Another solution that has been proposed is to increase the coefiicientof friction between the backs of the slips and the surface of the bowlof the casing head by rough machining the bowl. However, this solutionhas been a failure because it prevents the slips from gripping the pipeenough to hold the pipe from moving. To fully understand the reason forthis requires a consideration of the transient conditions occurringduring the setting of the slips.

The back of a slip is adapted to engage a support which is either at afixed radial distance from the surface of the pipe to be engaged by thefront of the slip or at most has but a limited amount of possible motionrelative thereto so that upon axial motion of the slip relative to thesupport in the direction the slip tapers down the consequent radialmotion of the slip toward the pipe will ultimately cause the teeth orother means on the front face of the slip to indent the pipe and preventrelative axial motion of the pipe and slip.

In the cases of the suspension of casing in a well head or theengagement of an overshot fishing tool with a pipe, there are usuallyonly two forces available for causing slip motion relative to thesupport:

(1) Weight of the slip;

(2) Friction between the slip and pipe as they move axially relative toeach other prior to the front face of the slip indenting the pipe.

In the case of packers and spears there usually is added to these theforce of friction between the pipe and spring loaded drag blocks orwiper springs, which in the following will be considered as part of theweight of the slips. The above mentioned two forces act axially andtheir components normal and parallel to the support surface vary as thetaper of the bowl. The greater the taper angle the larger the normalforce and the less the parallel force. Any frictional or analogous forceresisting relative motion between the slip and support parallel to thesupport surface must be overcome by the component of the aboveenumerated forces tending to move the slip parallel to the supportsurface. If the latter is insufi'icient the slip will not move relativeto the support and hence will not move in radially to indent the pipeand the slip will be inoperative.

The frictional resistance to relative motion of the slip and supportdepends on the normal force holding them in engagement. As previouslystated, this normal force is initially a component of the weight andpipe friction forces acting on the slip and increases as the taper angleof the support increases. Therefore, increasing the bowl taper angleboth lowers the parallel component of these forces and increases thenormal component, both changes reducing the net force tending to movethe slip.

The frictional resistance of slip motion also increases with increase ofthe coefiicient of friction for the engaged surfaces of slip andsupport.

4 As the slip moves relative to the support the radial motion of theslip relative to the pipe causes the pipe to begin to indent and aradial force due to the reaction of the pipe on the slip is added to theprevious friction force due to their relative motion. This increases thetoal frictional resistance to motion of the slip relative to thesupport. If the force of frictional resistance due to relative motion ofthe slip and pipe does not increase as fast or faster due to theindentation of the pipe than the frictional resistance to motion of theslip relative to the support, the latter will soon prevail and the slipwill stop moving relative to the support and hence will stop indentingthe pipe and the pipe will not be gripped by the slip enough to preventrelative motion of pipe and slip.

With a rough machined bowl, the coefiicient of friction is so large thateither the initial resistance to slip motion is sufficient to hold theslips stationary despite the force of the slip weight and pipe frictionor else the force of resistance to slip motion increases faster than theforce between pipe and slip and predominates before the pipe has beenindented sufficiently to be held against motion. In this latter case theslip merely removes a layer of scale and metal from the pipe as itslides through. It is the object of this invention to provide a devicefor anchoring to pipe that will overcome the difficulties previouslyoutlined of pipe bottle-necking collapse or bursting, which will bereliable and simple to operate, and which will be inexpensive and easyto manufacture.

According to the invention friction control means is provided betweenthe back faces of the slips and the surface of the slip bowl to causethe coefficient of friction to be initially low enough to cause theslips to set, that is, indent and hold the pipe against relative motion,and thereafter to increase to such a value that the downward and henceinward motion of the slips is insuflicient to cause reduction of casingdiameter beyond the permissible amount even when the maximum weight ofcasing is hung on the slips.

Other objects and advantages of the invention will become apparent fromthe following description of a preferred embodiment thereof, referencebeing bad to the accompanying drawings wherein:

FIGURE 1 is an elevation partly in section, of a well head incorporatinga casing suspension embodying the invention.

FIGURES 2A and 2B are enlarged sectional views showing portions of thecasing suspension illustrated in FIGURE 1, and illustrating the slipsthereof in unset and set positions respectively;

FIGURES 3 and 4 are sectional views on a still larger scale showingportions of the casing suspension in unset and set positionsrespectively;

FIGURES 5 and 6 are horizontal sections taken along lines 5-5 and 66 ofFIGURE 1;

FIGURE 7 is an elevation showing a casing hanger of the type illustratedin FIGURE 1;

FIGURE 8 is a top view of the casing hanger shown in FIGURE 7 andshowing a set of slips disposed therein;

FIGURES 9 and 10 are front and back views of one slip of a set of slipsembodying the invention, of the type shown in FIGURE 1.

FIGURE 11 is an enlarged fragmentary detail in vertical section througha slip and hanger showing a modification;

FIGURE 12 is a further enlargement of a portion of the detail shown inFIGURE 11;

FIGURE 13 is a view similar to FIGURE 11 showing a further modification;

FIGURE 14 is an enlargement of a portion of FIG- URE l3;

FIGURES 15 and 16 are views similar to FIGURE 14 showing two furthermodifications;

FIGURE 17 is a view similar to FIGURES 11 and 13 showing a furthermodification;

FIGURE 18 is an enlargement of a portion of FIG- URE 17;

FIGURES 19 and 20 are views similar to FIGURE 18 showing two furthermodifications;

FIGURE 21 is an elevation partly in vertical section, showing a wellhead embodying a modified form of the invention;

FIGURE 22 is a detail showing a portion of the Well head shown in FIGURE21;

FIGURE 23 is an enlarged vertical sectional view showing a portion ofthe apparatus shown in FIGURE 21;

FIGURE 24 is a vertical section showing an overshot embodying theinvention;

FIGURE 25 is a vertical section showing a spear embodying the invention;and

FIGURE 26 is a vertical section showing a permanent type packerembodying the invention.

Referring first to FIGURE 1 there is shown a casing head 30 secured tothe upper end of a string of casing 31. Supported by and sealed to thecasing head is the upper end of another string of casing 32 disposedinside the casing head and extending thereabove into the lower portionof tubing head 33. Casing 32 is also sealed to the tubing head.

Referring now also to FIGURE 7, the means for sealing between the casinghead 30 and casing 32 includes a casing hanger which comprises a hollowbowl 41 of generally circular cross section having upper and lower outercylindrical portions separated by a conical shoulder 42 adapted to seaton a similar conical shoulder 43 inside the casing head. The lower endof the'bowl 41 is conical on its exterior as shown at 44 to guide thebowl into place when it is lowered into the head.

As best shown in FIGURE 8, the bowl is preferably made in two halveswhich are pivotally connected together at one side by a spring steeldouble pintle hinge 45 whose pintles 46 are welded into recesses outinto the bowl above and below a channel 47, the channel being an easilymachined space for the pintles and hinge to Work in. At the oppositeside from hinge 46 a spring steel latch 48 is pivotally and snapconnected respectively to pins 49 mounted similarly to pins 46. A dowelpin 49" disposed in one half of the bowl adjacent latch 48 is adapted toenter a hole 50' in the other half of the bowl to help maintainalignment of the two halves of the bowl.

Referring againt to FIGURES 1 and 7, and also to FIGURE 5, to the upperend of the bowl 41 is secured a means for sealing between the casing andcasing head comprising a support ring 50, a compression ring '51 and aring 52 of rubber-like sealing material such as neoprene disposedtherebetween. The three rings of the sealing means are held together andto each other by means of a plurality of screws 53 screwed through therings into the top of bowl 41. The rings are free to slide up and downon the screws 53. The support ring 50 has a bevel surface 54 around itslower outer periphery adapted to seat on a conical shoulder 55 insidethe casing head 30. With the support ring thus seated, tension on screws53 due to load on the bowl causes the compression ring to move down andexpand the sealing material ring horizontally to seal between the casingand casing head. The compression ring 51 also has a bevel surface 56around its upper outer periphery onwhich bear lock screws 57, by meansof which the compression ring can be forced down or held down to make ormaintain the seal and retain the hanger in the casing head.

As shown in FIGURES 5 and 7, rings 50 and 51 are each preferably made intwo halves, and ring 52 is split adjacent one of the junctures of thetwo halves of rings 50 and 51. The part of ring 52 adjacent the otherjuncture of the two halves of rings 50' and 51 serves as a hinge. Sincering 52 is fairly stiff and tends to retain its circular shape no latchis needed for the part of the sealing means that opens up to receive thecasing.

Referring now to FIGURES 1, 9, and 10, the interior of bowl 41 isprovided with a recess having a conical surface 60 within which aredisposed a plurality of slips '61. Each slip is provided with a tappedrecess 62 which can be aligned with one of a plurality of holes 62through the bowl 41, whereby a screw, not shown, can be passed throughhole 63 into hole 62 to retain the slip in the bowl and hold it inelevated, i.e., retracted position as shown in FIGURE 2A. These screwsare removed after the hanger is placed around the casing and before itis lowered into the casing head. The slips are maintained in verticalalignment by the engagement of a pin 64 welded to one side of each slipwith a groove 65 in the adjacent slip.

The inner or front face of each slip is provided with a plurality ofteeth 66 which are preferably upwardly pointing, that is, the medians orlines connecting the midpoints of the crests with the midpoints of theroots point outwardly up. The teeth preferably are of modified buttressthread cross-section. In fact each set of slips is conveniently formedfrom an integral sleeve which is turned with an internal buttress threadbefore it is cut into four segments to form the slip-s.

On the outside or back face of each slip there are formed a plurality ofteeth 67. These are preferably downwardly pointing and also of modifiedbuttress thread cross-section and having flat crests 68 as best shown inFIGURE 3. These teeth are also conveniently formed by cutting a helicalthread on the exterior of a sleeve that is later cut into segments toform a set of slips. Although the teeth 67 are downwardly directed, theyare what may be termed unloading teeth, in that the angles between theteeth flanks 69 on the lower sides of the teeth and the base materialare obtuse angles. The teeth are also unloading with reference to theirupper flanks 70. By making the active areas of the teeth unloading, thatis, by making unloading the parts that engage the opposing metal of thehanger 41, there is no wedging action tending to make the teeth dig infarther when moved tnansversely, that is, parallel to the surface of theopposing metal. The combined area of the crests of teeth 67 is greaterthan the combined area of the crests of teeth 66.

Referring again to FIGURE 2A, in the unstressed condition the top ofbowl 41 is in contact with support ring 50- and the distance betweenbeveled surface 54 and shoulder 42 is less than the distance betweenshoulders 55 and 43. When the hanger is placed in the casing head itseats first on shoulder 55. Then, when the casing is lowered and theslips are pulled down in the bowl as shown in FIGURE 2B, the bowl seatson shoulder 43 and the screws 53 draw the compression ring 51 down toexpand the seal ring radially against the casing head and the casing toseal therebetween. This mode of automatic scaling is disclosed andclaimed in United States Patent No. 2,824,757 issued February 25, 1958.The seating of the bowl on shoulder 43 limits the degree of loading ofthe sealing means including the seal ring 52 and the tension screws 53.I

Referring now to FIGURES 3 and 4, there is illustrated the action of theback teeth 67 on the backs of the slips 61. As shown in FIGURE 3,initially the fiat crests 68 of the teeth slide down in the bowl 41 asload is applied by the front teeth of the slips gripping the casing.Then :as the load increases, the stress at the area of contact betweenthe crests 68 and the bowl 41 exceeds the yield point of the material ofthe bowl and the teeth 67 dig in as shown in FIGURE 4. The engagement ofteeth 67 with the bowl 41 retards further downward movement of the slipscompared to the movement that would take place if the backs of the slipswere smooth and thereby prevents excessive radial inward motion of theslips under maximum casing weight permissible so that the casing willnot be collapsed. The prevention of excessive deformation of the casingnot only insures that the casing will not be parted and that full gagetools can be passed therethrough, but also insures that the seal betweenthe casing and seal ring 52 will be maintained.

It is to be noted that slips are usually heat treated so as to make themhard and strong. This is to enable the front teeth 66 to bite into thecasing. It is therefore no extra trouble to provide hardened back teeth67 which are heat treated at the same time as the rest of the slip.Since teeth 67 are harder and stronger than the slip bowl, the yieldpoint of the slip bowl is lower than that of the slip teeth and onincreasing load the bowl yields while the teeth are still below theiryield point and the teeth bite into the bowl.

Referring now to FIGURES 11 through there are shown alternativeconstructions of the slips and bowl. In each of these cases the frontface of each slip 100 is provided with preferably upwardly directedteeth 101 to engage casing 102 the same as in the FIGURES l and 4embodiment. Also, the outside or back face of the bowl part 103 of eachhanger is provided with a steeply tapered seat 104 like the shoulder 42in the first described embodiment. Since these parts are the same ineach case, they are given the same reference numbers. The back faces ofthe slips and/or the front faces of the bowls are modified ashereinafter described.

In FIGURES l1 and 12, the back faces 105 of each of the slips is atapered surface of less taper than seat 104, the same as in the FIGURESl and 4 embodiment, but there are no teeth, the surface being smooth.Furthermore, the face 105 is of a hardness and strength more nearlyequal to that of the front face 107 of the bowl than in the FIGURES 1and 4 embodiment, preferably the hardness of the two faces being equaland less than that of teeth 101. This is accomplished by heat treatingonly the front or toothed face of each slip.

The face 107 of the bowl is of less vertical extent than the back ofeach slip; this being done to reduce the area of contact between thebowl and backs of the slips so as to provide high unit stresstherebetween. The area of contact is larger, however, than that of teeth101 with casing 102.

In operation, the teeth on the front faces of the slips first bite intothe casing as load is applied, the back faces of the slips moving downon the bowl and radially inwardly. Then when the unit stress on thecontacting surfaces of slips and bowl exceeds the yield points of themetal of slips and bowl, galling takes place followed by the productionof a plurality of heat and pressure welds between slips and bowl asshown in FIGURE 12. This tends to prevent further downward movement ofthe slips and hence prevents further rapid radial inward motion thereofas the slips bring the casing to rest. By proper choice of materials andareas of contact of slips and bowl for any given casing, the slips canbe made to stop their inward motion before bottle necking or crushing ofthe casing occurs.

In the embodiment shown in FIGURES 13 and 14, the slips are the sameshape as in FIGURE 11, but the front face 107 of the bowl 103 is not ofreduced vertical extent and is the same as in the FIGURES 1 and 4embodiment. As best shown in FIGURE 14, granular particles 108 of amaterial harder than either the bowl or the back faces of the slips,e.g. tungsten carbide particles of average diameter of inch are disposedbetween the slips and bowl. These are placed in a suitable vehicle suchas paint or grease or other sticky viscous fluid and applied, e.g. by abrush, to either or both of the contacting surfaces of slips and bowlbefore assembly. Preferably this application should take place justbefore the hanger is set in the casing head on completion of the well toinsure that none of the material is lost before use. The quantity ofgranular material used should be such that the area of contact of theparticles with the slips or the bowl is greater than that of the teethon the front faces of the slips with the casing.

In operation, as shown in FIGURE 14, the teeth on the front faces of theslips bite into the casing as load is applied causing downward andinward motion of the slips to cause them to dig deeper into the casing.Then as the unit stress on the bowl and the backs of the slips reachesthe yield point, the adjacent surfaces of slips and bowl yield causingthe granular particles to dig into both slips and bowl and bind themtogether to retard further downward motion of the slips as the slipsbring the easing to rest until the slips finally stop as full load isreached. As in any slip suspension, stopping of downward motion alsostops radial inward motion to stop further increase of radical stress onthe pipe held by the slips but according to the invention this isachieved more rapidly as the slips take the casing load so as to preventits collapse.

Referring now to FIGURES l5 and 16 there are shown two furthermodifications on the same general plan as the embodiment of FIGURES l3and 14. In FIGURE 15 the granular particles 109 are permanently attachedto the backs of slips 100, for example by sweating them on, eitherdirectly into the base metal or into a solder coating. Alternatively thegranules could be permanently affixed to the inner face of the bowl.Instead of using irregular particles, regular particles such as ballbearings could be used as shown at 110 in FIGURE 16, placed at regularintervals in holes 111 in the backs of the slips and staked intoposition; alternatively, the smooth particles could be similarly securedto the bowl. The operation of these embodiments is substantially thesame as that of the embodiments previously described.

Referring now to FIGURES 17 through 20 there are shown embodiments ofthe invention in which both the front face of the bowl and back faces ofthe slips are other than smooth. In FIGURES l7 and 18, these surfacesare provided with teeth having very wide gently sloping tooth flanks. Inoperation these teeth slip past one another as load is first applied tothe slips, with increasing depths of tooth crest sheared off untilfinally the width of the interengaging tooth crests is sufficient tohold the load. The slip teeth then hang on the bowl teeth and preventfurther rapid downward motion of the slips and thus further radiallyinward motion stops before there is collapse or excessive deformation ofthe casing.

FIGURES l9 and 20 illustrate other tooth forms which can be used inplace of the form shown in FIGURES l7 and 18. In FIGURE 19 the teethhave convex flanks and rounded crests. In FIGURE 20 the teeth haveconcave flanks and sharp crests. The operation of the embodiments shownin FIGURES l9 and 20 is similar to that of FIGURES 17 and 18. Preferablythe metals used for the back surfaces of the slips and the front face ofthe bowl in embodiments of FIGURES 17 through 20 will be of equal orsubstantially equal hardness and strength and of less hardness andstrength than that of the teeth on the front faces of the slips. Thismay be accomplished by heat treating the front or toothed face of eachslip.

Referring now to FIGURES 21-23, there is shown a further embodiment ofthe invention in which the casing is supported on slips 131 whose backfaces 132 seat directly in conical bowl 133 in the casing head 134. Theusual seal between the casing and casing head above the slips is shownat 135 between supporting ring 136 and compression ring 137.

As best shown in FIGURE 22, the conical bowl of casing head 134 has aplurality of dome shaped protuberances 140 formed thereon at preferablyregular intervals. These may be formed by adding material to the bowlwith an arc welding rod. The welded on material will be harder than thebowl and the backs of the slips.

The operation of the embodiment of the invention shown in FIGURES 21-23is similar to that of the previously described embodiments. Thepreferably upwardly facing teeth 141 on the front faces of the slipsgrip the casing as the casing is lowered and the slips move downwardlyand inwardly on the bowl 133. Then when the unit stress betweenprotuberances 140 and the back surfaces of the slips exceeds the yieldpoint of the slips, the pro tuberances dig int-o the slips and retardfurther downward motion thereof, thus reducing the total inward motionof the slips under full load and preventing excessive load from beingapplied tothe casing that might collapse it or cause it to bottle neck.

In this embodiment of the invention the slips should be hardened only ontheir front faces, leaving the backs of the slips soft enough for theweld metal to dig into the slips. However if it is desired to heat treatand harden the slips all over, the protuberances could be applied to thebacks of the slips instead of the face of the bowl, in which case thearrangement would be very nearly the same as in FIGURES 1 and 4 exceptfor the absence of a hanger. It will be understood that the hanger maybe eliminated or used with any of the various embodiments of theinvention heretofore described, the principal features of the severalembodiments being the nature of the contacting surfaces of the backs ofthe slips and the face of the bowl, whether the bowl is integral withthe casing head or is in a separate hanger. However certain embodimentsof the invention as respects the contact surfaces of the slips and bowlare better suited for use with a bowl and others without, and they havebeen shown in each case in the preferred combination.

In reviewing the foregoing embodiments of the invention it will be notedthat in all cases means is provided between the backs of the slips andthe bowl to control the coeficient of friction or perhaps moreaccurately the coefiicient of sliding resistance or ratio of the forcerequired to cause sliding of the slips on the bowl to the normal forcebetween them, that is, the force perpendicular to their contactingsurfaces. The ratio is controlled so as to increase rapidly whenever thenormal force reaches a predetermnied critical value. In this way thetotal sliding of the slips relative to the bowl is reduced, therebyreducing the radially inward motion of the slips to prevent collapse ofthe pipe held by the slips. In all cases the critical loading of theslips at which the coefiicient of friction increases would not only beless than that which corresponds to excessive pipe deformation butshould be greater than the loading needed to make the slips grip thepipe firmly.

The foregoing embodiments of the invention show its application to thesuspension of casing in a casing head. It is to be understood howeverthat this invention is of wider applicability and is useful whenever apipe is to be gripped by wedges and it is desired to limit the stress onthe pipe. The invention can be used to suspend tubing as well as casing.Although the gripping of the backs of the slips to the bowl renders theinvention of less utility where the suspension is not permanent, eg inthe case of drill pipe suspended in a rotary table, there maynevertheless be some instances where use of the invent-ion innonpermanent suspensions will be very useful. For example, P IGU RE 24shows an overshot used in fishing operations. The tools there shown areconventional except for the contacting surfaces of the slips 150 andbowl 151 which may be formed to provide a variable coefficient ofsliding resistance according to any of the methods previously describedso as to prevent collapse of the fish 152. As illustrated, slips 150 areprovided with fiat crested teeth 153 as in the FIGURE 1 embodiment.

Not only is the invention useful to prevent collapse of pipe but it canbe used to prevent its bursting as in the case of the fish spear shownin FIGURE 25. The spear is conventional except for the contactingsurfaces of the slips 160 and expander 161 which are formed to provide acoefiicient of sliding resistance increasing sharply before the loadreaches such a value as to cause bursting of pipe 162. Again, any of themethods previously described or other similar method can be used tocontrol the friction. As shown, flat crested teeth 163 are provided onthe back or inner faces of the slips, the teeth 164 on the front orouter faces of the slips being conventional, e.g., upwardly pointing. Itwill be noted that whether the slips move radially in or out under load,it is the vertical cylindrical face which has the ordinary teeth and theinclined or conical face at which the variable coefficient of frictionis provided. The vertical face, exposed to grip the load, is cal-led thefront face; the inclined face, lying against the bowl or expander orother support, is called the back face.

FIGURE 26 shows an embodiment of the invention in a permanent typeproduction packer which is conventional except for the areas of contactbetween the holddown slips 170 and upper expander 1'71, and between holdup slips 172 and lower expander 173 which are provided with means tocontrol the friction according to any of the methods previouslydescribed or similar methods, so as to prevent bursting of casing 175when packer 176 is expanded by pulling up on tubing 177. As shown, theslips are provided with flat crested back teeth 178, 17 9 as in FIGURE1.

Plain hold up or hold down releaseable packers for production and cementretaining and other applications can also be made embodying theinvention in a manner similar to that illustrated in FIGURE 26 for apermanent (nonreleaseable) type packer.

While preferred embodiments of the invention have been shown anddescribed, man-y modifications thereof can be made by one skilled in theart without departing from the spirit of the invention and it isintended to protect by Letters Patent all forms of the invention fallingwithin the scope of the following claim.

What is claimed is:

1. A pipe anchoring device comprising support means, segmented meansdisposed symmetrically around said support means, pipe gripping means onsaid segmented means coaxial with the axis of symmetry of said segmentedmeans and facing away from said support means, and pipe actuated meansactuated by the pipe moving in contact with the pipe gripping meansaxially in one direction relative to said support means to move saidsegmented means radially toward the pipe, said pipe actuated meansincluding smooth axially continuous surface areas on one of the twofirst said means disposed around said axis and equally flaring therefromin a direction opposite to said one direction and facing the other ofthe two first said means, said pipe actuating means further includingindenting means harder than said smooth surface areas and disposedaround the axis of said other of the two first said means and with aplurality of said indenting means in engagement with said smooth surfaceareas to gall said smooth surface areas when the normal forcetherebetween exceeds a certain value greater than that existing whensaid pipe gripping means engages the pipe sufiiciently to preventrelative motion of the pipe and pipe gripping means and less than apredetermined value corresponding to excessive radial deformation of thepipe, said indenting means having portions facing said one direction tohang on said surface areas when galled and resist motion of saidsegmented means relative to said support means in said one direction,said indenting means having portions dull compared to said pipe grippingmeans facing said smooth surface areas for movement relative theretowithout galling when said normal force is less than said predeterminedvalue, said indenting means comprising granular particles.

2. The (combination of claim 1 in which said indenting means comprisesgranular particles initially free to move relative to said segmentedmeans and support means.

3. The combination of claim 1 in which said indenting means comprisesgranular particles embedded in said other of the two first said means.

4. The combination of claim 1 wherein the granular particles of saidindenting means are made of tungsten canbide.

5. A pipe anchoring device comprising support means,

segmented means disposed symmetrically around said support means, pipegripping means on said segmented means coaxial with the axis of symmetryof said segmented means and facing away from said support means, andpipe actuated means actuated by the pipe moving in contact with the pipegripping means axially in one direction relative to said support meansto move said segmented means radially toward the pipe, said pipeactuated means including smooth axially continuous surface areas on oneof the two first said means disposed around said axis and equallyflaring therefrom in a direction opposite to said one direction andfacing the other of the two first said means, said pipe actuated meansfurther including indenting means harder than said smooth surface areasand disposed around the axis of said other of the two first said meansand embedded therein and with a plurality of said indenting means inengagement with said smooth surface areas to gall said smooth surfaceareas when the normal force therebetween exceeds a certain value greaterthan that existing when said pipe gripping means engages the pipesulficiently to prevent relative motion of the pipe and pipe grippingmeans and less than a predetermined value corresponding to excessiveradial deformation of the pipe, said indenting means comprising spacedirregular particles harder than said smooth surface areas and havingportions facing said one direction to hang on said surface areas whengalled and resist motion of said segmented means relative to saidsupport means in said one direction, said particles having portions dullcompared to said pipe gripping means facing said smooth surface areasfor movement relative thereto without galling when said normal force isless than said predetermined value.

6. The combination of claim wherein the irregular particles of saidindenting means are made of tungsten carbide.

7. A pipe anchoring device comprising support means, segmented meansdisposed symmetrically around said support means, pipe gripping means onsaid segmented means including sharp portions substantially coaxial withthe axis of symmetry of said segmented means and facing away from saidsupport means, and pipe actuated means actuated by the pipe moving incontact with the pipe gripping means axially in one direction relativeto said support means to move said segmented means radia'lly toward thepipe, said pipe actuated means including facing smooth axiallycontinuous surface areas on each of the two first said means disposedaround said axis and equally flaring therefrom in a direction oppositeto said one direction, said pipe actuated means further includingindenting means comprising loosely disposed irregular particles harderthan said smooth surface areas disposed between said smooth surfaceareas of the two first said means and engaging therebetween to gall saidsmooth surface areas when the normal force therebetween exceeds acertain value greater than that existing when said pipe gripping meansengages the pipe sufiiciently to prevent relative motion of the pipe andpipe gripping means and less than a predetermined value corresponding toexcessive radial deformation of the pipe, said particles having portionsfacing said one direction to hang on said surface areas when galled andresist motion of said segmented means relative to said support means insaid one direction, said particles having portions dull compared Withsaid pipe gripping means facing said smooth surface areas for relativemovement between said smooth surface areas without galling thereof whensaid normal force is less than said predetermined value.

8. The combination of claim 7 wherein the irregular particles of saidindenting means are made of tungsten carbide.

9. A slip having a general-1y segmental cylindrical face with sharpteeth on said cylindrical face and having an opposite face taperingrelative to the axis of said cylindrical face, said tapering face havingparticles of irregular size and surface configuration secured on saidtapering face in abutting surface contact with the outer surface thereofwith said particles being harder than the base material of said slip.

10. Annular segmented pipe anchoring wedge means having an axial pipereceiving passage therethrough, said wedge means comprising meansincluding sharp teeth disposed in said passage presenting a generallycylindrical pipe gripping surface, and means including particles ofirregular size and surface configuration secured on the exterior of saidwedge means in abutting surface contact therewith and presenting agenerally conical wedging surface.

11. A unitary construction slip including a generally segmentalcylindrical face with sharp teeth on said cylindrical face and having anopposite face tapering relative to the axis of said cylindrical face,said tapering face having particles of irregular size and surfaceconfiguration secured on said tapering face in abutting surface contactwith the outer surface thereof.

References Cited in the file of this patent UNITED STATES PATENTS1,852,695 Carroll Apr. 5, 1932 2,086,652 Volpin July 13, 1937 2,312,487Roach et :al. Mar. 2, 1943 2,490,512 Deely Dec. 6, 1949 2,576,528Matthysse Nov. 27, 1951 2,683,045 Brooks July 6, 1954 2,824,757 RhodesFeb. 25, 1958 FOREIGN PATENTS 41,478 Switzerland Aug. 8, 1907

9. A SLIP HAVING A GENERALLY SEGMENTAL CYLINDRICAL FACE WITH SHARP TEETHON SAID CYLINDRICAL FACE AND HAVING AN OPPOSITE FACE TAPERING RELATIVETO THE AXIS OF SAID CYLINDRICAL FACE, SAID TAPERING FACE HAVINGPARTICLES OF IRREGULAR SIZE AND SURFACE CONFIGURATION SECURED ON SAIDTAPERING FACE IN ABUTTING SURFACE CONTACT WITH THE OUTER SURFACE THEREOFWITH SAID PARTICLES BEING HARDER THAN THE BASE MATERIAL OF SAID SLIP.